title: Lung alveolar integrity is compromised by telomere shortening in telomerase-null mice.
abstract: Shortened telomeres are a normal consequence of cell division. However, telomere shortening past a critical point results in cellular senescence and death. To determine the effect of telomere shortening on lung, four generations of B6.Cg-Terc(tm1Rdp) mice, null for the terc component of telomerase, the holoenzyme that maintains telomeres, were bred and analyzed. Generational inbreeding of terc-/- mice caused sequential shortening of telomeres. Lung histology from the generation with the shortest telomeres (terc-/- F4) showed alveolar wall thinning and increased alveolar size. Morphometric analysis confirmed a significant increase in mean linear intercept (MLI). terc-/- F4 lung showed normal elastin deposition but had significantly decreased collagen content. Both airway and alveolar epithelial type 1 cells (AEC1) appeared normal by immunohistochemistry, and the percentage of alveolar epithelial type 2 cells (AEC2) per total cell number was similar to wild type. However, because of a decrease in distal lung cellularity, the absolute number of AEC2 in terc-/- F4 lung was significantly reduced. In contrast to wild type, terc-/- F4 distal lung epithelium from normoxia-maintained mice exhibited DNA damage by terminal deoxynucleotidyltransferase (TdT)-mediated dUTP nick end labeling (TUNEL) and 8-oxoguanine immunohistochemistry. Western blotting of freshly isolated AEC2 lysates for stress signaling kinases confirmed that the stress-activated protein kinase (SAPK)/c-Jun NH(2)-terminal kinase (JNK) stress response pathway is stimulated in telomerase-null AEC2 even under normoxic conditions. Expression of downstream apoptotic/stress markers, including caspase-3, caspase-6, Bax, and HSP-25, was also observed in telomerase-null, but not wild-type, AEC2. TUNEL analysis of freshly isolated normoxic AEC2 showed that DNA strand breaks, essentially absent in wild-type cells, increased with each successive terc-/- generation and correlated strongly with telomere length (R(2) = 0.9631). Thus lung alveolar integrity, particularly in the distal epithelial compartment, depends on proper telomere maintenance.
authors.affiliation: Saban Inst. for Research, Childrens Hospital Los Angeles, MS 35, 4661 Sunset Blvd., Los Angeles, CA 90027, USA.
authors.forename: Jooeun
authors.initials: J
authors.lastname: Lee
authors.forename: Raghava
authors.initials: R
authors.lastname: Reddy
authors.forename: Lora
authors.initials: L
authors.lastname: Barsky
authors.forename: Jessica
authors.initials: J
authors.lastname: Scholes
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Shi
authors.forename: Barbara
authors.initials: B
authors.lastname: Driscoll
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D004249:DNA Damage; D004549:Elastin / Q000378:metabolism; D005260:Female; D020287:In Situ Nick-End Labeling; D036341:Intercellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D018384:Oxidative Stress / Q000502:physiology; D010455:Peptides / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000378:metabolism / Q000473:pathology*; D037721:Pulmonary Surfactant-Associated Protein C; D012313:RNA / Q000235:genetics* / Q000378:metabolism; D020545:Respiratory Mucosa / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction / Q000502:physiology; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D016615:Telomere / Q000235:genetics* / Q000473:pathology*
chemical_list: D000199:Actins; D015415:Biomarkers; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D037721:Pulmonary Surfactant-Associated Protein C; C489680:Sftpc protein, mouse; C422952:telomerase RNA; D012313:RNA; D003094:Collagen; D004549:Elastin; D048031:JNK Mitogen-Activated Protein Kinases; D019098:Telomerase